Multioffice automatic telephone system



1 1927. Oct A. B. SMITH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM 10 Sheds-Sheet 1 Original Filed May 8. 1922 ur E5555 Efifh v 1927' A. B. SMITH MULTIOFFICE'AUTOMA'i'IC TELEPHONE SYSTEM Inuen 511- 1,645,549 Oct. 18, 1927. A. B. SMTH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM Original Filed May 8. 1922 10 Sheets-Sheet 3 misnlm fiffhur Beasley Efiflh 1 1927. Oct A. B. SMITH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Sheet 4 Original Filed May 8, 1922 Inuen UE- fiffhur BESSEH SW11 Oct. 18,1927. 1,645,549

A. B. SMITH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM Original Filed May 8, 1922 10 Sheeis-Sheet 5 H SW11 5 1 a w J ,0, 9 J W M BLIII 1 fi G ii -z 1 1927. Oct A. B. SMITH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM Original Filed May 8. 1922 10 Sheets-Sheet 6 fiffhur Basseg STE/.71 5% M. 517" Oct. 18, 1927. 1,645,549

A. B. SMITH MULTI-OFFICE AUTOMATIC TELEPHONE SYSTEM Original Filed May 8. 1922 10 Sheets-Sheet 7 18 1927. Oct A. B. SMITH MULTI-OFFICE AUTOMAT IC TELEPHONE SYSTEM 1O Sheets-Sheet 8 F Original Filed May 8. 192

--liw mfv HfThur Bessey EFITfl-L Patented Oct. 18, 1927.

UNITED STATES PATENT OFFICE.

ARTHUR BESSEY SMITH, OF EVANSTON, ILLINOIS, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE.

MULTIOFFICE AUTOMATIC TELEPHONE SYSTEM.

Application filed May 8, 1922, Serial No. 559,337. Renewed September 7, 1926.

The present invent-ion relates in general to multi-ofiice automatic telephone systems, but as to some of its features, is concerned more particularly with systems of the above named character in which the inter-oilice trunking is arranged so as to group the offices into a number ofseparate networks or geographical districts. In certain respects this case may be considered as an improvement on my prior application, Serial No. 550,451, filed April 7, 1922.

One object is the provision of new and improved trunking arrangements and improved cooperating equipment for mult-i-oflice telephone systems, whereby a call may be tentatively trunked to a plurality of districts, each of which contains ofiices having the first characters similar to offices in the other districts, and whereby the call may be routed subsequently to the right office in the proper district. I

Another object has to do with the circuit details of the various so called universal switches which are employed to carry on the principles of the invention. I

Still another object is the production of a new and improved method for combining two comparatively small groups'of trunks into one larger and more efficient group and for separating the two groups at a point where they diverge.

Still another object is the production of a new impulse relaying repeater which repeats all the impulses after the first series but does not repeat the first series of impulses.

The above pointed out objects, together with others not specifically mentioned at this time, will be explained fully hereinafter, reference being had to the accompanying drawings, comprising Figs. 1-12, inclusive.

Referring now to the drawings, Figs. 1-8, inclusive, show by means of the usual circuit diagrams asufficient amount of the apparatus in a system embodying the principles of the invention to enable the same to be understood; Fig. 9 shows the front part of the calling device, or dial as it is commonly called, with which each subscribers telephone is equipped; Fig. 10 is a map showing the location of the various ofiices of the system disclosed; Fig. 11 is a trunking diagram showing how calls are trunked from one of the offices to every other office in the system; and Fig.12 is a layout showing how the sheets of drawings including Figs. 1-8, lnclusive, are joined together.

Of the equipment shown in Figs. 1-8, incluslve, the equipment shown in Figs. 1-4, lnclusive, is assumed to be in Lincoln, Figs. 10 and 11; theequipment shown in Figs. 5 and 6 is assumed to be in Medbury; the equipment shown in Fig. 7 in Pontiac ;'-and the equipment shown in Fig. 8 in Market.

Referring now particularly to Figs. l-8, inclusive, and Fig. 11, the automatic substations A and A, Fig. 11, of which the circuits are shown in Figs. 1 and 8, respectively, are identical with each other, and are of the usual automatic type, having talking, signalllng, and switch controlling instrumentalities.

The line switches C and C, Fig. 11, in which the lines of substations A and A, respectively, terminate as shown in Figs. 1 and 8, are also identical with each other, and are of the well known rotary type in which the wipers have no normal position and move in a forward direction only.

The selectors D, EE inclusive, FF inclusive, (Pr-G inclusive, and H, Fig. 11, of which the selectors D, G, G E, F, G G and H are shown in Figs. 1, 46, inclusive, 7, and 8, are mechanically of the well known vertical and rotary type and accordingly th-eir'bank contacts are arranged in horizontal rows or levels. The circuits of these selectors are all identical with each other, with the usual exception that, whereas those winch are associated with trunks from distant oflices do not have release trunk conductors carried back with the talking conductors, the selectors which receive traffic from local switches do. The circuits of the selectors G and E, which are a local selector and an incoming selector, respectively, are shown complete in Figs. 4 and 5, respectively, and

will be described fully hereinafter.

The connector J, Figs. 8 and 11, is mechanically identical with the selectors. Its circuits, however, differ from those of a selector, and are shown in full in Fig. 8.

The secondary switches SS-SS", inclusive, Fig. 11, of which the switches SS SS SS SS inclusive, SSQ-SS, inclusive, and SS *SS inclusive, are shown in Figs. 2-7, inclusive, are mechanically identical with each other and with the rotary line switches C and C, hereinbefore described. The circuits of all secondary switches are identical with each other, with the exception of the secondary switch S5", Figs. 6 and 11, and are changed only slightly from the circuits of the primary line switches C and C. The slight change is necessary in some instances in order to prevent the switching relay of one of these switches from energizing immediately upon the switch being seized, owing to ground being placed upon the release trunk conductor thereof when the switch is seized. However, barring the previously mentioned secondary switch SS", the cir cuits of all the secondary switches are made alike in order to permit the switches themselves to be interchanged when necessary. The circuits of the secondary switch SS" are identical (with the circuits of any of the other secondary swltches, with the exception of an added pair of contacts on the switching relay thereof and an added wiper, the functions of which will be described.

Regarding the universal switchers US-US, inclusive, Fig. 11, of which the universal switchers US, US and US are shown in Figs. 1-3, inclusive, respectively, each comprises the necessary relays and a cont-rolling switch. Each of these controlling switches is of simple construction. The controlling switch associated with the universal switcher US, Fig. 1, for example, comprises a stepping magnet 80, wiper 82 and, associated back contacts, release magnet 81, and ofl normal contacts 7 9. The wiper 82 is moved step by step in one plane by stepping magnet 80, and is subsequently restored to normal by release magnet 81. Off normal conteats/79 are normally open, as shown, and close upon Wiper 82 being moved from its normal position. The circuits of the universal switchers USUS, inclusive, while fundamentally similar to each other, differ somewhat from each other in circuit detail, depending upon the situation in which they are used. The switchers US, US and US which are shown in Figs. 1, 3, and 2, respectively, are chosen as being typical ones. The circuits of these switchers will be explained fully hereinafter.

The repeaters R-R, inclusive, Fig. 11,

are repeaters of the usual automatic type and each is provided with a repeating coil and the necessary relays as may be seen in Figs. 2, 3, 4, 6, and 7, in which the circuit of the repeaters R-R, inclusive, R and R are shown in detail.

The digit absorbing repeaters DAR-DAR inclusive, Fig. 11, of which the digit absorbing repeater DAR is shown in full in Fig. 5, are similar to the repeaters R, R, etc with the exception that each of the former is arranged so as to absorb the first digit or train of impulses delivered to it after it is seized. The following impulses, however, are repeat ed in the usual manner to the distant oflice.

The bi-level repeater BLR Figs. 11 and 6, is an ordinary repeater so far as its repeating functions are concerned. This repeater has an added relay which, together with cooperating circuits, enables an impulse of current to be sent over one side of the trunk momentarily when the repeater is seized from one path but not when the repeater is seized from the other path. This repeater repeats impulses over the associated trunk in the usual manner after having been seized.

The tratlic separator TS, Figs. 11 and 7, is connected with the opposite end of the trunk to which the bi-level repeater BLR is connected. This trafiic separator has suitable relays and cooperating circuits to enable it to choose one or the other of the outgoing paths, depending upon Whether or not the upper trunk conductor leading 'to it is grounded momentarily when the bi-level repeater BLR is seized.

Referring now particularly to Fig. 9, the exposed part of the calling device shown therein is provided, not only with the digits 1 to 0, but also with the letters of the alphabet as shown. It will be noted that the letters of the alphabet are placed in order in the holes of the calling device from the first to the tenth with the exception that the letter I, which is often mistaken for the digit 1, is placed in the first hole, and the letter O, which resembles the digit 0, is placed in the tenth hole of the calling device. These two exceptions are made so that no harm results when a subscriber mistakes the letter I for the digit 1 or the letter O for the digit 0. In the directory, each subscribers number comprises the first three letters of the ofiice name and four digits, for example MARket-1234. The first three letters M, A, and R, or the ones to be dialed, are capitalized, so as to enable the subscriber to see at a glance which letters he must use when calling a number.

Referring now particularly to Fig. 10, which, as before stated, is a map showing the approximate relative location of the oflices in the present system, and also the names of the various offices, the oflices shown therein are divided into four groups which will be hereinafter called districts. This drawing shows also the trunking which is used to extend calls from Lincoln to each of the other offices, giving an idea as to the manner in which the calls are distributed. Each of the trunks shown, of course, is only one of a group, there being a sufiicient number to handle the traific. It may be stated that there are direct trunks (of which only a few are shown) from each office to every other oflice in the same district, thus.weaving the offices in each district together into an integral network. The scheme used for inter-district trunking in the presentinstance is to provide direct trunks from the originating oflice to the nearest or one of the nearest offices in the district for which the call is intended, which oflice then takes on the character of a switching center. After a call has been trunked into a distant switching center, it is completed to the desired otfice over the regular inter-ofiice network local to the district. For example, on a call from Lincoln to Maburn, the call is trunked first to Dunham and then to Maburn, the trunk from Dunham to Maburn being used, not only in completing local calls from Dunham to Maburn, but also in completing inter-district calls.

The names of the various ofiices shown are assumed to have belonged to these oifices since manual equipment was first installed and it is assumed further that a change of ofice names, when the system was changed from manual to automatic, was undesirable and was not made. That being the case, special trunking arrangements are necessitated in order to enable a number of otfices to be reached by way of a common switching center without making it necessary for calls to be trunked over such long and devious paths that the efliciency gained by providing switching centers is lost on account of the intricate trunking network necessitated. For example, it will be noted that the first two letters M and A of Market, which ofiice is located at the right hand end of the system, are the same as the first two letters M and A of Maburn, which ofiice is located at the extreme left hand of the systems. It is evident that, when a subscriber in Maburn or Market is being called, it cannot be definitely determined until the third letter is dialed whether the call is intended for Maburn or for Market.

In order to meet these conditions, universal switchers have been placed in each ofiice, and when a subscriber dials a letter which does not determine definitely to which district the call is going, a universal switcher is seized, which switcher takes a trunk to each of the districts to which the call might go. Allthe trunks, except the one that is actually needed to complete the call, are released by the universal switcher as soon as the subscriber has called enough of the number to determine which trunk will be used.

Since more than one letter is associated with each digit appearing on the face at the calling device used, the letters of two oflices do not need to be the same in order to conflict with each other. In order to enable the conflicting otfice names to be seen at a glance, the numerical e uivalent of the first three letters in each 0 ce name iswritten underneath the name of the oifice, Fig. 10. For example, the numerical equivalent of the first three letters of Polk is 605 and the numerical first selector D for example.

equivalent of the firstthreele ttersof North 7 Referring now which is a trunking diagram showing how the problems presented in Fig. 10 are solved, the trunking will be explained more in detail. In order to do this, it will beassumed that the subscriber at substation A in Lincolndesires to call the subscriber at substation A in Market. Upon the receiver being removed at substation A, the individual line switch 0 picks out an idle first selector, the

to the calling of the first letter M in the desired number, the selector D raises its wipers to the fifth level the letter M appearing in the fifth hole of the calling device Fig. 9)

and rotates them in search of an idle trunk.

It will be assumed that the trunk extended to the universal switcher US is the first one found to be idle and consequently the one selected. When the trunk which extends to the universal switcher US is seized, the said universal switcher US connects up the secondary switch SS and the secondary switch SS but. does not connect up the secondary switch SS for the time being. The secondary switches SS and SS operate to seize idle trunks, which trunks it will be assumed are the ones shown. That being the case, the selector E in Dunham and the selector E in Medbury, are prepared for operation in the usual manner.

In response to the calling of the second letter A in the desired number, the selector E in Dunham and the selector E in Medbury, which selectors are controlled by the repeaters R and B, respectively, raise their Wipers to the first level and select idle trunks, the trunks extending to the selectors F and F for example, and in response to the calling of the third letter R in the desired number, the selectors F and F raise their wipers to the seventh level and rotate them in search of idle trunks. The seventh level of the selector F is dead, and conse quently its trunk selecting operation is of no avail at this time. The selector F, upon rotating, selects an idle trunk in the seventh level, the trunk extending to the secondary switch SS for example. The secondary switch SS", upon operating, selects an idle trunk, the one extending to the bi-level repeater BLR for example. The group of trunks to which the trunk associated with the bi-level repeater BLR belongs performs the work of two groups of trunks. Each of these trunks is accessible from two paths, and, upon one of these trunks being seized, one or the other of the switches associated therewith in the distant oflice is connected up by a tralfic separator such as the traffic separator TS, depending upon from which path the repeater is seized. In the present case, since the repeater BLR is seized from In response particularly to Fig. 11,

the upper path, the second switch SS is connected up by the traflic separator TS. The switch SS, upon being connected up to the inter-oifice trunk, selects a trunk to Market, the trunk extending to the selector G by way of the repeater R for example.

In the universal switcher US, a recording device which has recorded the part of the number called, upon responding to the callin of the third letter R, disconnects the secon ary switch SS whereupon the trunk to Dunham is freed, and cuts off its own line relay and does not respond to the calling of the remaining part of the number.

In response to the calling of the four digits in the desired number, the connection is extended to the desired line in the usualmanner, by way of the selectors Gr and H and the connector J.

Assuming now that the subscriber at substation A is calling a subscriber in Maburn, the call proceeds as in the previously described case upon the dialin of the first two letters M and A in the desired number. Assuming that the call takes the same path as in the previous example and is extended to the selector F in Dunham and to the selector F in Medbury, these two selectors F and F, are raised to the second level upon the calling of the third letter B in the desired number. The second level of the selector F is dead and, consequently, the trunk selecting operation of the said selector F is of no avail at this time. The second level of the selector F, however, is not dead, and consequently the said selector F, upon rotating, selects an idle secondary switch, the secondary switch SS for example, which secondary switch, upon operating, selects an idle repeater, the repeater R for example. That being the case, the distant selector in Maburn associated with the repeater R is prepared for operation in the usual manner.

The universal switcher US, upon recording the third letter B in the desired number, cuts ofi the secondary switch SS whereupon the connection to Medbury is released in the usual manner.

In response to the calling of the four digits in the desired number, the connection is extended to the desired line in Maburn by means of the usual automaticswitches such as are shown in Market.

Assuming now that the subscriber at substation A desires to call another subscriber whose line terminates in the same oflice as the line of substation A, the line switch C trunk extending to the universal switcher US to be the one selected, the secondary switches SS and SS are connected up in the usual manner.

In res onse to the calling of the second letter I 1n the oflice name, the selectors in Dunham and Medbury to which the connection has been extended, the selectors E and E for example, raise their wipers to the first level and select idle trunks, which trunks it will be assumed are the ones extending to the selectors F and F.

In response to the callin of the third letter N in the desired num er, the selectors F and F in Dunham and Medbury respectlvely, raise their wipers to the sixth level and rotate them in search of idle trunks; The trunk selecting operation of the selector F in Dunham is of no avail, the sixth level thereof being dead. The selector F in Medbury, however, selects an idle secondary switch, the secondary switch S for example, and as a result the connection is extended by way of a bi-level repeater, the bilevel repeater BLR for example, trafiic separator TS, and the secondary switch SS in Pontiac, to a thousands selector, the thousands selector (it for example.

In the universal switches US, the before mentioned recording device, upon recording thethird letter dialed, disconnects the secondary switches SS and SS, whereupon.

the connection to Dunham and the connection to Pontiac by way of Medbury are released in the usual manner. As another 'result of the recording device in the universal switcher US operating in response to the third letter N, the secondary switch SS is connected up and. upon operating, selects an idle thousands selector, the thousands selector G for example. In response to the calling of the four digits in the desired number, the connection is extended to the desired line by way of the thousands selector G','and a hundreds selector and a connector (not shown). The universal switcher US which through its associated secondary switches SS and SS has access to trunks to Attington and to Dunham, connects up the secondary switch SS immediately upon being seized, but in case the second and third letters of Atlantic are called, the secondary switch SS is not connected up at all. However, if the third letter also is T, the secondary switch SS is disconnected, vwhereupon the connection to Dunham is released. At the same time, the secondary switch SS is connected up, whereupon a trunk to Attington is seized.

Similarly the universal switcher US", which through its secondary switch SS has access to direct trunks to Beverly and through its secondary switch SS has access to Cedar by way ofthe switching center Blazon, connects up the secondary switch SS immediately upon being seized thereby seizin a trunk to Blazon. If the second and t ird letters of Cedar are called, the secondar switch SS is not connected up; the trun to Beverly is not seized; and t e connection is extended to the desired subscriber in Cedar in the usual manner. However, if the second and third letters of Beverely are called, the trunk to Blazon is released and-the trunk to Beverly 1s se1zed, upon the calling of the third letter, and the connection is completed in the usual manner, upon the calling of the four dlgits 1n the desired number.

The universal switcher US connects up the associated secondary switch SS immediatel upon being seized and if either the secon letter A of Saxony or the second letter E of Seminole is called the universal switcher US does not record the next letter in the number, but cuts ofi its line relay since the calling of the second letter A or the sec ond letter E determines definitely that the call is going to Saxony or to Seminole and not to South. If the second letter called,

after the universal switcher US is seized, is 0 instead of A or E, the secondary SWltClr SS is cut off, but the secondary switch SS is not connected up unless the third letter called is the third letter U of South.

Still another situation arises in connection with offices North, Polk, and Pontiac.- When the universal switcher US is seized, upon the calling of either the letter N or-the letter P, it immediately connects up the sec ondary switches SS and SS, thereby seizing trunks to Dunham and to Medbury, and? upon the calling of the second letter O of either North, Polk, or Pontiac, the connection is extended to a second selector in Medbury, the selector F for example. In Dunham, the connection is extended to a digit absorbing repeater by the operation of the selector E, for example, to the digit absorbing repeater DAR, by way of the secondary switch SS This digit absorbing repeater,

7 upon being seized, closes a control circuit for the distant associated selector in North immediately in the usual manner. This repeater, however, is arranged so as not to repeat the first series of impulses to the associated selector. If the third letter called is N, the connection is extended to Pontiac by way of a path which, for. example, includes the secondary switch SS, bi-level repeater BLR, trafiic separator TS, and the secondary switch SS and extends to a thousands selector such as the selector G If the third letter called is L, the connection is extended to North by way of a secondary switch and a repeater, such as SS and R". In either of these two cases the connection to Dunham is released upon the calling of the third letter. However, if the third letter called is R, the connection to Medbury is released and the digit absorbing re eater DAR in Dunham, u on absorbing t e first digit repeated to it a ter it is seized, is made ready to repeatthe followin digits.

It will be un erstood that certain calls may be completed that do not pass through any universal switcher. One example of such a call will now be given. Assuming that the subscriber at substation A desires to converse with a subscriber whose line terminates in Upland, and assuming that his line is extended to the selector D upon the removal of his receiver, the said selector D raises its wipers to the eighth level and selects an idle secondary switch, the secondary switch SS for example, upon the calling of the first letter U inthe desired number.

The secondary switch SS, upon operating,

selects an idle re eater, the repeater R for example. That being the case, the associated selector E in Medbury is prepared for operation.

Upon the calling of the second letter P in the desired number, the selector E in Medbury raises its wipers to the sixth level and selects an idle secondary switch, the second- .sorbing repeater DAR for example, that being the case, the distant associated selector in Upland 1s prepared for operation in the usual manner.

Upon the calling of the third letter L in the desired number, five impulses are delivered to the repeater DAR but, as hereinbelOO fore' described, the first series of impulses sent to the repeater after it'has beenseized are not repeated over the outgoing trunk.

In response to this series of interruptions the repeated DAR is made ready to repeat the succeeding trains of impulses over the outgoing trunk.

In response to the calling of the four digits in the desired number, the connection is ex-' tended to the desired line in Upland in; the usual manner; It is thought'tha't the foregoing is'sufiicient to give a general understandin of the system and, accordingly, a detailed escription of the operation of the apparatus shown in Figs. 1-?8, inclusive, will now be given.

Call from Lz'hcoln oflice to Market office.

For this purpose it will be assumed that the subscriberat substation A, Fig.,1, whose line terminates in Lincoln, Figs. 10 and 11, desires to converse with the subscriber at substation A, Fig. 8, whose line terminates '4 A in Market, Figs. 10 and 11, and whose-number is Market 3456.

When the receiver is removed at substation A, a circuit is closed over line conductors 2 and 3 for line relay 6 of the line switch 0. Line relay'6, upon energizing,

at a point between the two.

places round upon private normal conductor 4;, t ereby making the calling line busy immediately to the connectors which have access to it. The placing'of ground upon private normal 4 conductor 4 also closes a circuit for switching relay 5 and stepping magnet 7 in series. As a further result of the energizat-ion of line relay 6, it connects, at armature 11, test wiper 14 to the circuit of switching relay 5 and stepping magnet 7 The operation now depends upon whether the trunk upon which the wiper 13-15, inclusive, of the switch are standing is busy or idle. If it is idle, switching relay 5 energizes immediately, but assuming it to be busy, there is a ground potential on the test contact thereof; switching relay 5 is short circuited; and stepping magnet 7, which interrupts its own circuit, is operated in the manner of a buzzer to advance the switch wipers step by step in search of an idle trunk. Assuming that the trunk terminating in bank contacts 16-18, inclusive, is the first one to be found idle, switching relay 5, being no longer short circuited after test wipers 14 arrives upon the ungro-unded test contact 17, energizes in series with stepping magnet 7. Stepping magnet 7, however, does not energize at this time on account of the high resistance of switching relay 5. Upon energizing, switching relay 5 opens the test circuit and prepares the holding circuit at armature 9; and at armatures 8 and 10 disconnects line conductors 2 and 3 from the winding of line relay 6 and ground, respectively, and extends them by way of the working contacts of these armatures, wipers 13, and 15, bank contacts 16 and 18, and trunk conductors 19 and 21 t0 the upper and lower windings of the line relay (not shown) of the selector D, which selector is denoted by the dotted rectangle bearing that reference character. In response to the energization of the line relay of the selector D, the switch D is prepared for operation and a ground potential is placed upon release trunk conductor 20, thereby establishing the usual holding circuit for switching relay 5 of the line switch C, before the slow act-ing line relay 6 has had time to deenergize.

The calling subscriber now turns the dial of his calling device or sender S, the front part of which is shown in Fig. 9, in accordance with the first letter M in the name of the oifice in which the desired line terminates, thereby producing five interruptions in the circuit of the line relay '(not shown) of the selector D. In response to these five interruptions being produced in its line relay,

' the selector D raises its wipers 2224, inclusive, to the fifth level and rotates them in search of an idle trunk. It will be assumed that the trunk comprising conductors 32-34, inclusive, and extending to the universal switcher US, is the one seized. That being the case, line relay 36, upon energizing over the calling subscribers loop, closes a circuit for release relay 37 at armature 47. Release relay 37, upon energizing, prepares a locking circuit for relays 40 and 41, at armature 49; prepares a circuit for stepping magnet at armature 50; and at armature 48 places ground upon release trunk conductor 33, thereby establishing the usual holding circuit for the line switch C and the selector D. As a further result of the energization of line relay 36, it closes at armature 16 a circuit for impulse relays 68 and 69 in multiple. These impulse relays, upon energizing, close local bridges across the associated trunk conductors at armatures 76 and 77.

In response to the closing of the local bridge across conductors 91 and 93 by armature 76 of impulse relay 68, line relay 102 of the secondary switch SS upon energizing, places ground upon release trunk conductor 92 at armature 111; closes a circuit for switching relay 101 and stepping magnet 103 in series at armature'110; and at armature 109 connects test wiper 113 to the circuit of switching relay 101 and stepping magnet 103 at a oint between the two. The secondary switcii SS now selects an idle trunk in the same manner as described hereinbefore for the primary line switch C. Assuming that the trunk extending to the repeater R is the first one found to be idle, switching relay 101, being no longer short oircuited, energizes when test wiper 113 arrives upon bank contact 116; opens the test oircuitand prepares the holding circuit at armature 107; places a shunt around armature 110 and its working contact at armature 106; and at armatures 105 and 108 disconnects conductors 91 and 93 from line relay 102 and from ground, respectively, and extends them by way of wipers 112 and 114, bank contacts 115 and 117, and conductors 118 and 120 to the upper and lower windings of line relay 126 of the repeater R. Line relay 126, upon energizing, closes, a circuit for release relay 127 at armature 128. Release relay 127, upon energizin places ground upon release trunkv conductor 119 at armature 130, thereby establishing the usual holding circuit for switching relay 101 of the secondary switch SS As a further result of the energization of line relay 126, itplaces a bridge across the inter-oflice trunk conductors 131 and 132 at armature 129. whereupon line relay of the associated selector E, Fig. 5, in Medbury. Figs. 10 and 11, energizes and closes a circuit for release relay 166 at armature .176. Release relay 166, upon energizing, prepares a circuit for switching relay 169 at armature 177 and at armature 178 opens a point in the circuit of release magnet and vertical magnet 172.

prepares a circuit for 1 Returning now to the universal switcher US, Fig. 1, as a result of the local bridge being placed across conductors'94 and 96 at armature 77 by impulse relay 69, the associated'secondary switch SS operates in the usual manner to select an idle repeater. In this case it will be assumed that the repeater R is the one selected. That being the case, the linerelay of the said repeater, upon energizing, in addition to closing a circuit for the associated release relay, closes a bridge across the associated trunk conductors,

' whereupon the selector E in Dunham, Fig.

11, is prepared for operation in the usual manner.

Returning again to the universal-switcher US, Fig. 1, it will be noted that no impulse relay is provided for the trunk conductors of the secondary switch SS'*, and consequently the said switch is not operated for the time being.

The calling subscriber now operates his calling device in accordance with the second letter A in the name of the desired office, thereby producing one interruption in the circuit of line relay 36 of the universal switcher US. Upon deenergizing in response to this interruption produced in its circuit, line relay 36 opens the circuit of impulse relays 68 and 69 at armature 46, whereupon the interruption is relayed to the circuits controlled by these relays at armatures 76 and 77.

Relay 126 of the repeater R, upon responding to the impulse relayed to it by impulse relay 68, interrupts the circuit of line relay 165 of the selector E momentarily. Line relay 165, upon deenergizing, closes a circuit for vertical magnet 172 as follows: From ground by way of the resting contact of armature 184 and said armature, armature 176 and its resting contact, armature 178 and its working contact, relay 167, and vertical magnet 172 to battery. By the operation of vertical magnet 172, which magnet receives one impulse at this time, the wipers 186488, inclusive, are raised opposite the first level of bank contacts. Relay 167, which relay it may be pointed out is slow acting so as to cause it to hold up during a series of interruptions delivered to vertical magnet 172,'is energized in series with vertical magnet 172 at this time, and at armature 17 9 closes a circuit for stepping relay 168 upon the closure of off normal contacts 175. Stepping relay 168, upon energizing, prepares acircuit for rotary magnet 173 at armature 181, and at armature 180 closes a locking circuit for itself. A fraction of a second after the termination of the vertical movement of the switch wipers, slow acting relay 167 deenergizes and completes the circuit of rotary magnet 173. Rotary magnet 173, upon energizing, advances the wipers 186-188, inclusive, into engagement with the first set of bank contacts in the level opposite which they are raised, at the same time opening the circuit of stepping relay 168. Stepping relay 168, upon deenergizing, opens the circuit of rotary magnet 173 at armature 181. Rotary magnet 173, upon deenergizing, closes its interrupter contacts 17 4 a ain. From this point the operation depen s upon whether the trunk terminating in the first set of contacts is busy or idle. If it is idle, switching relay 169 energizes immediately, but if it is busy, switching relay 169 is short circuited by the ground potential which is present upon the test contact thereof, and stepping relay 168 energizes again, whereupon rotary magnet 173 energizes also and the wipers are advanced into engagement with the next set of bank contacts. This alternate operation of stepping relay 168 and rotary magnet 173 continues until an idle trunk is reached. When an idle trunk is reached, which trunk it will be assumed is the one extending to the se lector F, switching relay 169, being no longer short circuited, energizes in series with stepping relay 168. Stepping relay 168, however does not energize at this time owing to the high resistance of switching relay 169. As a result of the energizati-on of switching relay 169, it removes ground from armature 176 of line relay 165 at armature 186, thereby opening the circuit of the slow acting release relay 166; opens the test circuit and prepares the holding circuit at armature 183; and at armatures 182 and 185 disconnects the incoming trunk conductors 131 and 132 from the windings of line relay 165 and extends them by way of wipers 186 and 188, the bank contacts with which these wipers are in engagement, and the associated trunk conductors to the upper and lower windings of the line relay of the selector F. The line and release relays (not shown) of the selector F now energize and the latter prepares the switch foroperation and places ground upon the associated release trunk conductor, thereby establishing the usual holding circuit for switching relay 169 of the selector E before the slow acting release relay 166 has had time to deenergize.

In the repeater B, Fig. 4, the line relay thereof, upon deenergizing momentarily in response to the interruption relayed to it by armature 77 of impulse relay 69 of the universal switcher US, interrupts the circuit of the line relay of the distant associated selector E in Dunham, Fig. 11. When this occurs, the selector E operates in the usual manner to raise its wipers to the first level and rotate them in search of an idle trunk. In this case, it will be assumed that the trunk extending to the selector F is the first one sponse to the interruption produced in its circuit by the calling subscriber, 1n addltion to opening the circuit of impulse relays 68 and 69 as hereinbefore pointed out, closes the following circuit for stepping magnet 80: From ground by way of the resting contact of armature 45 and said armature, armature 47 and its resting contact, armature 50 and its working contact, relay 38, and stepping magnet 80 to battery. By the operation of stepping magnet 80, which magnet receives one impulse at this time, wiper 82 is advanced into engagement with the first associated bank contact 84. Relay 30 is energized in series with vertical magnet 80 and maintains the circuit of release magnet 81 open after the closure of off normal contacts 79, which closure occurs as soon as wiper 82 is moved from its normal positlon. After the end of the stepping movement, series relay 38, upon deenergizing, completes at armature 51 a circuit for release magnet 81 by way of off normal contacts 79. Release magnet 81, however, having a comparatively heavy armature, the retaining spring of which is stifliy adjusted, is not able to energize immediately. A branch of the circuit of release magnet 81 extends by way of armature 83 and its resting contact, wiper 82, blank contact 84, armature 52 and its resting contact, relay 40, and relay 39 to battery. Relays 40 and 39 energize in series over this circuit. Relay 40, upon energizing, closes a locking circuit for itself and for relay 39 at the lightly adjusted armature 54, and prepares circuits for seizing relays 65-67, inclusive, at armature 5557, inclusive, respectively. Relay 39, upon energizing, opens its initial circuit and that of relay 40 at armature 52 and at armatures 53 disconnects relay 41. Release magnet 81 energizes, a fraction of a second after its circuit and that of relays 39 and 40 are closed and after sufficient time has been allowed 'for relay 40 to close the previously described locking circuit, thereby disconnecting wiper 82 at armature 83 and allowing it to be restored to normal position, the circuit of release magnet 81 being opened at off normal contacts 79 when wiper 82 reaches normal position.

One result so far accomplished, by the calling of the first two letters in the desired number, is that the connection has been extended over two paths, one path extending to the selector F in Dunham by way of the selector E, and the other path extending to the selector F in Medbury by way of selector E. Another result accomplished is that the universal switcher US has recorded the second letter dialled and is in readiness to record the third letter dialled and to make a corresponding definite choice of the route to be used in completing the connection.

The subscriber at substation A now 0perates his calling device in accordance with the third letter R in the desired number, thereby producing seven interruptions in the circuit of line relay 36 of the universal switcher US. These seven interruptions are relayed by relays68 and 69 to the selectors F and F, Fig. 11, by way of the repeaters R and R. The selector F, Fig. 5, in response to the seven interruptions produced in the circuit of its line relay, raises its wipers 198-200, inclusive, step by step until they come to rest opposite the seventh level of bank contacts, after which it rotates them insearch of an idle trunk in. the usual manner. Assuming the trunk terminating in bank contacts 215-217, inclusive, com.- prising conductors 227-229, inclusive, and extending to the secondary switch SS", to be the first one found to be idle and consequently the one selected, line relay 281 of the switch SS" is energized in response to the switch being seized. Upon energizing, line relay 281 closes the usual circuits, whereupon the switch wipers are advanced into engagement with an idle trunk in the usual manner. It will be assumed that the trunk extending to the bi-level repeater BLR is the first one found to be idle and conseq'uent ly the one selected. That being the case, switching relay 280, upon energizing in the usual manner at the end of the trunk hunting operation, extends conductors 227-229, inclusive, throughto the corresponding conductors of the bi-level repeater BLR. As a further result of the energization of switching relay 280, it places a ground potential upon the discriminating wiper 282 at armature 279. This ground potential extends by way of discriminating conductor 283, resting contact of armature 284 and said armature, upper trunk conductor 277, armature 407 and its resting contact, resting contact of armature 411 and said armature, and line relay 401 of the traflic separator TS to battery: Upon energizing, line relay 401 places ground upon release trunk conductor 416 of the secondary switch SS by way of armature 406 of line relay 402 and its resting contact, thereby closing a circuit for switching relay 403. Relay 403, upon energizing, disconnects line relay 402 from trunk conductor 278 at armature 408; disconnects line relay 401 from trunk conductor 277 at armature 407, and at armatures 407 and 409 and their working contacts connects trunk conductors 277 and 27 8 with trunk conductors 415 and 417 of the secondary switch SS. The line relay of the secondary switch SS upon energizing over conductor 277, starts the trunk hunting operation of the switch in the usual manner at its two upper armatures, and at its lower armature places ground upon release trunk conductor 416, thereby establishing a holding circuit for switching relay 403 before lease relays of t e repeater R, upon energizing, close a bridge across the associated outgoing trunk conductors and establish the usual holding circuit for the traflic separator TS and the secondary switch SS.

In response to the bridge being closed across the associated inter-office trunk conductors by the line relay of the repeater R the line and release relays (not shown) 0% the selector Gr energize, thereby, preparing the switch for operation in the usual manner.

Returning now to the bi-level repeater BLR, line relay 270, upon energizing in response to the repeater being seized, prepares the usual bridge for conductors 277 and 278 at armature 274. This bridge,however, is open at another point as may be seen. As a further result of energization of line relay 270, it closes a circuit for release relay 271 at armature 273. Release relay 271, upon energizing, places ground upon the associated release trunk conductor at armature 276, thereby establishing the usual holding circuit for the selectors E and F and the secondary switch S8. As a further result of energization of release relay 271, it closes a circuit for relay 272 at armature 275. This relay is designed and wound so as to allow time for the trafiic separator TS to function as hereinbefore described before the said relay 272 operates. Upon energizing, relay27 2 removes the discriminating ground from trunk conductor 277 and completes the usual bridge across conductors 277 and 278 at armature 284.

In Dunham the selector F, (Fig. 11,) to which the connection to Dunham has been extended, raises its wipers to the seventh level, in response to the seven interruptions produced in the circuit of its linerelay by the line relay of the repeater R in response to the calling of the third letter in the desired number, and rotates them in search of an idle trunk in the usual manner. It will be noted that the seventh level of the selector F is dead. Consequently, the trunk selecting operation of the said selector F is of no avail at this time.

In the universal switcher US, Fig. 1, line relay 36, uponresponding to the seven interruptions produced in its circuit upon the calling of the third letter of the desired number, in addition to opening the circuit of impulse relays 68 and 69 at armature 46, as hereinbefore explained, sends seven impulses of current to stepping magnet 80 y way of series relay 38. By the operation of stepping magnet 80, the wiper 82 is advanced step by step until it comes to rest upon the seventh associated bank contact 88. Relay 38 is energized in series with stepping magnet 80, an being slow acting, retains its armature attracted throughout the stepping movement, thereby maintaining the circuit of release magnet 81 open at armature 51 after ofi normal contacts 79 close upon wiper 82 being moved from its normal position. At the end of the stepping movement, series relay 38, upon deenergizing, closes the circuit of release magnet 81 at armature 51 by way of oil normal contacts 79. A branch of this circuit extends by way of armature 83 and its resting contact, wiper 82, the seventh associated bank contact 88, working contact of armature 55 and said armature, and seizing relay 65 to battery. Upon energizing, seizing relay 65 closes a locking clrcuit for itself at the l1ghtly adjusted armature 73, before its initial circuit is opened by release magnet 81. Release magnet 81, upon energizing, disconnects wiper 82 at armature 83 and restores it to normal position in the usual manner, the circuit of release magnet 81 being opened at ofl' normal contacts 79 when wiper 82 reaches normal position. As a further result of the energization of seiz ing relay 65, it connects release trunk conductor 33 with release trunk conductor 92 of the secondary switch SS at armature 73; connects line conductors 32 and 34 with conductors 91 and 93 at armatures 71 and 75, and at armature 72 closes a circuit for out ofl relay 35. Cut off relay 35, upon energizing, removes ground from armature 47 of line relay 36 at armature 45, thereby opening the circuit of release relay 37, and at armatures 43 and 44 disconnects conductors 32 and 34 from the windings of line relay 36. Line relay 36, upon deenergizing, opens the circuit of impulse relays 68 and 69 at armature'46. Impulse relay 68, upon deenergizing, removes the local bridge from across conductors 91 and 93 at armature 76, leaving line relay 126 of the repeater R under the direct control of the calling substation. Impulse relav 69, upon deenergizing, removes the local bridge from across conductors 94 and 96 at armature 77, where upon the connection to Dunham is released in the usual manner. Release relay 37 upon deenergizing, opens the locking circuit of relays 39 and 40 at armature 49, whereupon relays 39 and 40 deenergize, and at armature 48 removes ground from release trunk conductor 33, leaving the said conductor grounded by way of the holding circuit which extends back from armature 130 of release relay 127 of the repeater R, Fig. 4.

The calling subscriber now operates his calling device in accordance with the first digit 3 in the desired number, thereby pro ducing three interruptions in the circuit of line relay 126 of the repeater R. These interruptions are relayed at armature 129 to line relay 270 of the bi-level repeater BLR, Fig. 6, and from thence to the mcoming selector G, Fig. 8, by way of the repeater B, Fig. 7. The selector Gr now raises its wipers to the thlrd level and rotates them in search of an idle trunk. In the resent case it will be assumed that the trunl; extending to the selector H is the first one found to be idle and consequently the one selected. That being the case, the selector'H is prepared for operation in tht usual manner.

In response to the calhn of the second digit 4 in the desired num er, the selector H raises its wipers to the fourth level and receives them in search of an idle trunk. It will be assumed that the trunk extendin to the connector J is the first one foun to be idle and cons uently the one selected. That being the case, ine relay 433, upon energizing in response to the seizure of the connector J, closes a circuit for release relay 434 at armature 450.. Release relay 434,

= upon energizing prepares a circuit for vertica magnet 471 and opens a point in the circuit of release magnet *470 at armature 453; places ground upon armature 458 of busy relay 438 at armature 452.; and at armature 451 places ground upon release trunk conductor 431, thereby establishing the usual holding circuit for the selectors G and H.

In response to the calling of the next dlglt 5 in the desired number, five interruptions are produced in the circuit of line relay 433 of the connector J. Each time line relay 433 deenergizes in response to one of these interruptions, it sends an impulseof current to vertical magnet 471, the first lmpulse of current being sent over the following circuit: From ground by way of armature 450 and its resting contact, armature 453 and.

its working contact, resting contact of off normal spring 469 and said spring, relay 435, and'vertical magnet 471 to battery. By the operation of vertical magnet 471, the wipers 481483, inclusive, are raised step by step until they stand opposite the fifth level of bank contacts, which is the level in which the line of substation A terminates. Relay 435 is energized in series with vertical magnet 471 and, being slow acting, retains its armature 454 attracted throughout the vertical movement, thereby maintaining its own circuit and that of vertical magnet 471 intact after the 01f normal springs shift as they do upon the first vertical step. At the end of the vertical movement, slow actin relay 435, upon deenergizing, shifts the impulse circuit from the vertical to the rotary magnet at armature 454.

The calling subscriber now operates his calling device in accordance with the next and last digit 6 in the desired number,

whereupon six interruptions are produced in the circuit of line relay 433 of the connector J. Each time line relay 433 deenergizes in response to one of these interruptions, it sends an impulse of current to rotary magnet 472 by way of the following circuit. From ground by way of armature 450 and its resting contact, armature 453 and its workin contact, normally open contacts *controlled by ofl' normal spring 459, armature 454 and its resting contact, resting contact of armature 459 and said armature, armature 466 and its resting contact, and rotary magnet 472 to battery. By the operation of rotary magnet 472, the wipers 481-483, inclusive, are rotated step by step until they come to rest upon the sixth set of bank contacts in the fifth level, which set comprises bank contacts 484-486, inclusive. Relay 439 is energized in multiple with rotary magnet 472 and, being slow acting, retains its armature attracted throughout the rotary movement. Upon energizing, relay 439 disconnects test wiper 482 from the upper winding of switching relay 440 and connects it to busy relay 438 at armature 461,

and at armature 462 places a shunt around armature 459 and its resting contact so as torender its own circuit and that of stepping magnet 472 independent of armature 459 which armature is attracted by busy relay 438 1n case test wiper 482 is rotated over grounded test contacts.

It will be assumed first that the line of substation A is busy when called. That hemg the case, test contact 485 is grounded and busy relay 438 is accordingly energized when test wiper 482 arrives upon the test contact of the called line. That being the case, relay 439, upon deenergizing at the end of the rotary movement, disconnects itself and rotary magnet 47 2 from the impulse Zil circuit at armature 462 (armature 459 having been operated) and at armature 461 opens the initial circuit of and completes a locking circuit for busy relay 438, the locking circuit being as follows: From ground g formed thereby that he cannot obtain the desired connection for the time being. Upon hearing this busy tone, the calling subscriber replaces his receiver, whereupon the entire connection is released in a manner to be hereinafter described.-

- It will be assumed now that the line of 

